linux-kernel - Re: [PATCH 1/1] tty: fix up atime/mtime mess, take four

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Date:	Fri, 06 Mar 2015 05:16:14 -0800
From:	Raymond Jennings <shentino@...il.com>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	john_paul.perry@...atel-lucent.com, stable@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/1] tty: fix up atime/mtime mess, take four

On Fri, 2015-02-27 at 18:40 +0100, Jiri Slaby wrote:
> So check the absolute difference of times and if it large than "8
> seconds or so", always update the time. That means we will update
> immediatelly when changing time. Ergo, CAP_SYS_TIME can foul the
> check, but it was always that way.

If I may ask, what is supposed to happen normally when you write to a
tty device?  I always thought the tty device was treated just like a
normal file wrt. timestamps.

Now I see a patch for 8 seconds something.
> 
> Thanks John for serving me this so nicely debugged.
> 
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> Reported-by: John Paul Perry <john_paul.perry@...atel-lucent.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: <stable@...r.kernel.org> # all, as b0b885657 was backported
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> ---
>  drivers/tty/tty_io.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index e07f35e14fa2..e31b18a6d576 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -1032,8 +1032,8 @@ EXPORT_SYMBOL(start_tty);
>  /* We limit tty time update visibility to every 8 seconds or so. */
>  static void tty_update_time(struct timespec *time)
>  {
> -	unsigned long sec = get_seconds() & ~7;
> -	if ((long)(sec - time->tv_sec) > 0)
> +	unsigned long sec = get_seconds();
> +	if (abs(sec - time->tv_sec) & ~7)
>  		time->tv_sec = sec;
>  }
>  


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